Ther were a few soft spots when I bought the boat 5 years ago so I knew I would eventually have to address the situation. But since I had many other priorities, I kinda forgot about it untill last summer when water started to make it's way inside the cabin when it rained. When I started investigating I quickly came to the conclusion that the only way to properly fix the issue was to remove the entire roof and start from scratch. Turned out it was a good decision because I realized it was even worse than I thought. The core of the starboard wall was completely rotten so I had to rebuild that too. It's a massive project but it's not as bad as it looks (that's what I keep saying to myself anyway!). It's mostly basic carpentry and fiberglass skills. And a lot of time.

Posting a few pictures from first half of the project. I'll post some more once completed in a couple of weeks.

Greetings,
Mr. F. Hmmmm. Looked pretty much due for some attention in the first 3 pictures. Subsequent shots...VERY nice. A bit of technical information if you will. What material and how are you attaching the filler blocks on the cabin sides? What material for replacement "beams/studs"? Looking pretty good so far.

Thanks Mr. Firefly! I used polyester resin to attach to filler block and once cured I glassed over them (2 layers of fabric). Not sure about the materiel for the beams to be honest with you. Got some left over cuts from a local lumber yard for a few bucks. It's hard wood for sure, either maple or ash from what I can tell. I'm water proofing the beams and the plywood with diluted resin. It should be solid and durable enough once glassed over.

We never use polyester resin for any repairs, epoxy only. The extra cost is not that much and the results and longevity are tremendously better. Wood seldom rots when coated with epoxy even under a fresh water leak. Poly on the other hand will hold water against the wood and cause it to rot. It's inabilty to adhere to wood is legendary. Even inferior wood incapsulated in epoxy is better than the best wood with polyester.

It takes a brave man to even contemplate starting a project of that scope, I can only imagine what was going through your mind as you tore away the first piece of roof. Just looking at the pictures makes the hair bristle on the back of my neck. Congrats!

Try an experiment. Take two 2" by 8" piece of glass cloth and place them on wax paper.
Soak one with polyester resin the other with epoxy.
the next day, try to make a circle out of them. The poly will crack with the slightest bend.
It doesn't flex which is why placing it over wood is a bad idea. Water will always get to the wood and rot it.
The epoxy cloth will make a circle.

WHen I pulled the poly and glass cloth off my boat, it came up in big sheets because it never really sticks to the wood and over time releases.

Hi,
I know you're copping some heat over the choice of resin and I Don't mean to be rude or negative or anything so please dont take it that way.

I am questioning the "patch work" style timber application you have got going on. I am currently building a plywood boat as we speak and IMO and from experience, having gaps in between timber and behind cloth in not the desired outcome for longevity based on moisture, rot prevention and for ease of fairing.

I have found it is advantageous and think you would too, to have a full piece and bend it, as apposed to making pieces fit like that!

Is it that, that is all that is available or is there another reason?

Perhaps there is a reason I should be keeping my small off cuts myself!

Greetings,
Whilst I agree with the epoxy rather than polyester comments and observations, the fact is the job IS being done. <edit> I just remembered...I did almost the same thing on a 34' MT years ago. If you look at pic. #6, that bottom row of plywood pieces fits into a slot, as it were, to give the screws holding on the interior piece of teak trim some place to "bite". I vaguely recall putting a layer of FG mat in there and wedging in short pieces of ply like a sandwich (original outer cabin sides, resin soaked mat, ply, resin soaked mat, original inner lip). Rather than use blocks of plywood right up to the inner roof, I opted to glass that area with several alternating layers of mat and cloth giving a final thickness of 1/4" or so. I glassed in ply around the port to give THOSE mounting screws a place to "bite" as well. I think I used polyester as well. <end edit>
Mr. H. I suspect reasons for the "patchwork" style might be: That's what was there originally as evidenced by the "shadows" left on the inside of the remaining FRP cabin sides (pics' 4&6); there is a curvature to the cabin sides and although it would be stronger to replace in one piece, replacing in smaller pieces is quite a bit easier.
As I mentioned in post #4 " Seal her up well and keep her dry and you're good to go." Keep her dry the operative term. Breakdown of adhesion and cracking are problematic with polyester in this application but again, the repair/rebuild IS being done. Kind of late in the game for "coulda, woulda, shoulda".

Greetings,
Whilst I agree with the epoxy rather than polyester comments and observations, the fact is the job IS being done.
Mr. H. I suspect reasons for the "patchwork" style might be: That's what was there originally as evidenced by the "shadows" left on the inside of the remaining FRP cabin sides (pics' 4&6); there is a curvature to the cabin sides and although it would be stronger to replace in one piece, replacing in smaller pieces is quite a bit easier.
As I mentioned in post #4 " Seal her up well and keep her dry and you're good to go." Keep her dry the operative term. Breakdown of adhesion and cracking are problematic with polyester in this application but again, the repair/rebuild IS being done. Kind of late in the game for "coulda, woulda, shoulda".

Yeah I saw how it was done originally but clearly that didn't work too well now did it lol ... Case in point, this project :-)

Was interested to see what the OP had to say about it. There may have been a good reason that I too could use in my project.

There are millions of boats built with polyester resin in direct contact with wood. While polyester resin may not be as good a glue as epoxy it is far more flexible to work with. It wets out glass cloth and mat better and working time is adjustable independent of temperature. Epoxy shrinks, sags out of vertical lamination's and is harder to sand. Epoxy expands and contracts differently then polyester so patchs often get hair line cracks between the polyester and epoxy. Would you weld an aluminum boat with steel welding rod? Epoxy is harder to sand so it make fairing epoxy patchs more difficult. Epoxy is stronger when used for structural components like dagger boards , rudders masts, or lifting foils. Vacuum bagged in a controlled environment. But for a bulkhead and cabin roof, come on, why make the job ten times harder than it already is.

Polyester is only 87% waterproof and epoxy is 98% or so as proved by UW in their studies on blisters. They took a 30' FRP boat, weighed it, placed it in the ocean and left it sealed up. 12 months later it was 1000 pounds heavier. When on the hard it lost the water. The water went inside the entire hull with capillary action the same as placing a white flower in a dyed water and watching it change colors.

When they were fiberglassing wood hulls with poly in the late 60's it causes major problems. I read where a Chris Craft sunk in the gulf stream because a sheet of glass came off the bottom and wrapped the props at speed which resulted in holeing the boat.

Poly is not flexible after it's hard. Wood flexes so of you encapsulate wood completely with lots of glass cloth and resin, you're good. Just a single layer, you're not.

As adhesives, epoxies bond in three ways: a) mechanically, because the bonding surfaces are roughened; b) by proximity, because the cured resins are physically so close to the bonding surfaces that they are hard to separate; c) ionically, because the epoxy resins form ionic bonds at an atomic level with the bonding surfaces. This last is substantially the strongest of the three. By contrast, polyester resins can only bond using the first two of these, which greatly reduces their utility as adhesives and in marine repair.